Update Introduction

[milesfrain]

The Functional JavaScript section currently reads:

Libraries such as UnderscoreJS allow the developer to leverage tried-and-trusted functions such as map, filter and reduce

Should probably update this to note lodash, ramda, fp-ts, and sanctuary.

However, functional programming in JavaScript has its own disadvantages: JavaScript is verbose, untyped, and lacks powerful forms of abstraction.

Readers may ask "what about TypeScript?", so we should explain that TypeScript isn't a "sound" solution for types.

Some more language comparison details here: https://discourse.purescript.org/t/language-highlights/1471

We could also possibly give a whirlwind tour of some of the advanced type features (targeting Haskell, Elm, and TypeScript users) with a disclaimer not to worry if the section may be confusing, since it will all be addressed in the upcoming chapters. Another option is to link to language comparisons and cheatsheets purescript/documentation#334.

A more detailed outline can be found in #193 (comment)

[milesfrain]

If you prefer to learn by reading examples, the purescript, purescript-node and purescript-contrib GitHub organizations contain plenty of examples of PureScript code.

Todo - convert these to links